So the Ops Manual gets changed and specifies One Pilot is designated the PIC and the other as SIC....then the logging of time is as Round suggests but without the Ops Manual being changed the logging of time even if done as you suggest less a Manual Change then one Pilot cannot log any time?
What Regulation you basing that your position upon?
Is a Bell 212/412 or an S-76 a Single Pilot Aircraft or a Two Pilot Aircraft.